The present disclosure relates generally to wound healing, and more particularly to systems and methods for supplying oxygen to a wound to accelerate the healing of damaged tissue and/or promote tissue viability.
When tissue is damaged and a wound results, a four phase healing process begins, and optimal metabolic function of cells in the tissue to repopulate the wound requires that oxygen be available for all of these phases of wound healing. Furthermore, the more layers of tissue that are damaged, the greater the risk is for complications to occur in the wound healing process, and difficult-to-heal wounds can encounter barriers to the wound healing process and experience delays in one or more of the last three phases of wound healing. For example, one of the most common contributing factors to delays in the healing of wounds such as venous leg ulcers, diabetic foot ulcers, and pressure ulcers, is the problem of chronic wound ischemia. Chronic wound ischemia a pathological condition that restricts blood supply, oxygen delivery, and blood request for adequate oxygenation of tissue, which inhibits normal wound healing.
One conventional standard of care for treating difficult-to-heal wounds involves the use of an advanced wound dressing, or a combination of advanced wound dressings, that provide a dressing treatment system. The advanced wound dressing may be positioned on the wound site and, in some cases, the surrounding intact skin, to provide a wound site enclosure. The advanced wound dressing typically includes materials having properties for promoting moist wound healing, managing wound exudate, and helping control wound bioburden. Those material provided in combination operate to produce limited moisture vapor permeability, and the more occlusive the dressing, the lower the amount of ambient air (and thus a respective lower amount of oxygen) that is available to the wound site.
100% oxygen exerts a partial pressure of 760 millimeters (mm) of mercury (Hg), and ambient air includes about 21% oxygen, so ambient air exerts a partial pressure of oxygen of about 159 mm Hg. A typical advanced wound dressing or wound dressing system utilizing materials that provide limited moisture vapor permeable operates to impacts the available oxygen for the wound site, thereby limiting the partial pressure of oxygen at the enclosed wounds site to about 10-60 mm Hg. Fresh air (and its associated higher oxygen amount) is then only provided to the wound site when the dressing is changed, and dressings may remain covering the wound site for up to seven days before a dressing change is required. As such, the limited moisture vapor permeability of advanced wound dressings produce a reduced oxygen wound environment that works against the optimal metabolic function of cells to repopulate the wound during all the phases of wound healing.
Specific examples of conventional systems and methods to provide tissue oxygenation for difficult-to-heal wounds include the intermitted or continuous application of topical hyperbaric oxygen to the wound site. Intermittent topical hyperbaric oxygen treatment systems involve providing a sealed extremity or partial body chamber, along with a connected source of pure oxygen at a relatively high flow rate, and positioning the wounded limb or body area in the sealed extremity chamber or partial body chamber. The oxygen source will then supply the chamber with up to 100% oxygen at flow rates that may exceed 300 liters per hour, pressurizing the interior of the chamber at up to 1.05% normal atmospheric pressure, thereby topically increasing the available oxygen for cellular processing at the affected wound site. For example, during oxygen application, the partial pressure of oxygen exerted inside the sealed extremity or partial body chamber may attain 798 mm Hg, and may be applied for about 90 minutes. These and similar methods of applying intermittent topical hyperbaric oxygen are restrictive, cumbersome, can only supply oxygen to the affected area intermittently with no systemic application, and only provide for a minimal increase in atmospheric pressure (about 5%). Therefore, the effects of the oxygen therapy on wounds using these methods tend to be minimal, which is evidenced by the lack of commercial success of topical hyperbaric oxygen extremity chambers.
Other conventional systems and methods to provide tissue oxygenation include disposable devices that provide for the transmission of gases in ionic form through ion-specific membranes in order to apply supplemental oxygen directly to a wound site. These devices are typically battery powered, disposable, oxygen supplemented bandages that are provided directly over the wound site, and utilize electrochemical oxygen generation using variations of a 4 electron formula originally developed for NASA. In such systems, the amount of oxygen that can be applied to the wound is typically in the range of 3 to 15 milliliters per hour, and desired oxygen flow rates are generated by utilizing corresponding, preselected battery sizes with predefined amperages. As such, these devices are either “on or off”, and do not have the ability to deliver a varying or adjustable oxygen flow or oxygen flow rate without obtaining a new device and/or a different battery having an amperage that will produce the desired flow rate. The utilization of fixed, non-variable oxygen flows and oxygen flow rates introduces corresponding limitations in the treatment of different sizes and types of wounds, and tends to result in the wound treatment system being oversized or undersized for the wound to which it is being applied.
The inventors of the present disclosure co-invented systems and methods that address the issues with the conventional wound treatment systems discussed above. For example, U.S. Pat. No. 8,287,506 and U.S. Patent Publication No. 2016/0082238 describe wound treatment systems that provide for low dose tissue oxygenation and continuous oxygen adjustability to wound site(s) to create a controlled hyperoxia and hypoxia wound environment for damaged tissue, accelerates wound healing, and promotes tissue viability. Those systems and methods operate by monitoring pressure information that is indicative of a pressure in a restricted airflow enclosure that is located adjacent a wound site (e.g., provided by a wound dressing), and using the pressure information to control power provided to an oxygen production subsystem in order to control an oxygen flow that is created by the oxygen production subsystem and provided to the restricted airflow enclosure. In some embodiments, those wound treatment systems include a flow sensor that measures the oxygen output of the oxygen production subsystem, with a pressure sensor downstream of the flow sensor that measures the pressure that may be utilized to control the oxygen flow created by the oxygen production subsystem as discussed above.
However, the inventors of the present disclosure have discovered that such wound treatment systems suffer from a number of issues. For example, the flow sensor utilized with such wound treatment systems is relatively large (currently approximately 36 mm by 20 mm), relatively expensive (currently approximately $60 USD), consumes a relatively high amount of energy (up to 40 milliamps (ma)), and requires “plumbing” (i.e., tubing that connects the flow sensor to the oxygen flow(s) that it measures) that takes up space in the wound treatment system chassis and results in a larger chassis than would otherwise be required absent the flow sensor. Furthermore, it has been discovered that oxygen production subsystem utilized with such wound treatment systems may provide greatly reduced oxygen production as humidity decreases, which can result in deficient wound site oxygen supply, and can cause the wound treatment systems to increase the power provided to the oxygen production subsystem to a level that can damage the oxygen production subsystem.
Accordingly, it would be desirable to provide an improved wound treatment system.